This invention relates to protection of oxidizable materials or devices used in glass-melting furnaces. More particularly, the invention relates to an oxidizable molybdenum (moly) electrode inserted through the batch of a vertical glass-melting furnace. Other devices and applications are also disclosed.
In a conventional electric glass-melting furnace, electrodes are coupled to a source of electrical power and placed in contact with a bath of molten glass. Electrical energy flows between the electrodes and dissipates energy in the form of Joule heating in the molten glass for melting glass-forming batch materials deposited on and floating atop the bath. Such electrodes may be inserted through openings in wall portions of the furnace, or may be directly placed in contact with the molten glass from above or through the layer of batch floating thereon as in the case of cold crown electrical melters.
In many conventional glass-melting furnaces moly is used as the electrode material. However, because moly has a relatively low oxidation temperature of about 500.degree. C., complex protection devices are required to shield the electrodes from deterioration by contact with ambient oxygen or oxygen trapped in the glass-forming batch materials and/or other corrosive agents thereon. Such devices include water-cooled stainless steel sleeves and/or specially fabricated glass contact refractory sleeves which surround the electrode. These devices are expensive and somewhat short lived. Further, water cooling tends to dissipate energy intended for glass-melting purposes and has a deleterious effect on melting energy efficiency. Conventional protection devices tend to be heavy and cumbersome and are not easily adjusted or replaced, thereby diminishing their versatility. Glass quality may also be affected by contamination of the glass by materials forming the protective devices which materials eventually corrode and become mixed with the glass in the furnace.
The present invention utilizes a relatively inexpensive and long-lived system for directly immersing moly rods into a bath of thermoplastic material. The moly rods are protected from oxidation without complicated peripheral apparatus. The system may be operated without cooling, and thus, energy utilization is enhanced. Further, the moly rods are supported in a relatively simple holder thereby facilitating adjustment and replacement.
It should be realized that the present invention is also applicable to other devices which may be directly immersed in a bath of molten glass as, for example, stirring devices, oxygen sensors and thermocouples. Also other oxidizable materials are contemplated (e.g. tungsten, rhenium, columbium, etc.), as long as the oxidizable portions thereof are protected in the manner set forth herein. However, in order to simplify the disclosure herein, reference will mainly be made to the advantages of the present invention relative to moly electrodes. It is intended, however, that such other alternatives are to be considered part of the invention.